The present invention pertains to injection molding of a tie that is useful for forming a loop for retaining a bundle of elongated articles, such as cables. Such a tie is commonly known as a cable tie.
One type of tie includes an elongated tongue with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth extending along one broad side of the tongue, and a second set of ratchet teeth on the other broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue, the sides including a movable pawl that is hinged at one side of said opening and an abutment surface that is at least in part directly opposite across the opening from the pawl, with at least one tooth being disposed on the abutment surface for engaging the second set of ratchet teeth when the tip of the tongue has been inserted through the opening with the second set of ratchet teeth facing the abutment surface, and wherein the pawl has at least one pawl tooth disposed for engaging the first set of ratchet teeth when the tip of the tongue has been inserted through said opening with the set of ratchet teeth facing the pawl. This type of tie may be injection molded by a method comprising the steps of (a) providing a mold that includes mold parts including a cavity in the general shape of the tie, wherein one of the mold parts includes a core section that forms the surface of the pawl that includes the at least one pawl tooth and that forms at least a part of the abutment surface that is directly opposite the at least one pawl tooth; (b) injecting molten plastic material into the mold cavity; (c) solidifying the plastic material in the mold cavity to form the tie; and (d) ejecting the solidified tie from a mold. In a prior art mold used for injection molding small ties, the core section is so thin in the region that lies directly between the tip of the at least one pawl tooth and the directly opposite part of the abutment surface that the core section cracks in such region after repetitively injecting the molten plastic material into the mold cavity under high injection pressure, whereby at least the core section must frequently be replaced. FIGS. 1 and 2 show this thin region 10 of the core section 12 of such a prior art mold part 14, with the thin region 10 being bounded on opposite sides by a first surface 16 defining the surface of the pawl that includes the at least one pawl tooth and a second surface 18 defining at least the part of the abutment surface that is directly opposite the at least one pawl tooth.